Paperboard food trays are typically formed by compressing cut out paperboard blanks between two mating dies.
One problem with the process of compressing paperboard between two dies is that it is difficult to align the typically lightweight blank precisely in the desired location between the two dies. One result of misalignment may be the formation around the rim of the tray of flanges having non-uniform and unsightly variations in width. The conventional way of dealing with the difficulty in aligning blanks is to cut the flat paperboard into a blank which is larger than that which is needed to make the final product, deform the tray between the two dies, and introduce an additional step called post-trimming which includes trimming the outer edges of the deformed tray to the dimensions desired. This is not only an additional step but also introduces additional material, investment and labor expense due to the waste of paper and the additional machinery or manpower needed to perform this step.
The dies which are conventionally used consist of a lower die which is fixed in position (typically at an angle to horizontal so that the blanks can be gravity fed onto the die) and an upper die which is hydraulically or mechanically raised and lowered to mate with the lower die. The blank is fed onto the lower die and intended to slide down the surface of the die and come to rest against a series of guiding projections, the purpose of which is to guide and hold the blank in a desirable position prior to deformation. Sometimes, unfortunately, the blank may slide only part way down the die and get prematurely caught on one of the guiding projections or between them and stop in that position. At other times the blank may stop just short of one of the guiding projections instead of seating against it as intended. Then when the upper die compresses the blank, the outer edges of the formed tray are not equal all around the tray and post-trimming is necessary.
Therefore, there is a need for a blank positioning apparatus which eliminates the additional cost of post-trimming the deformed blank by accurately locating the blank at its desirable position prior to deformation.